This project is a study of the mechanism responsible for narcotic-induced respiratory depression. Utilizing iontophoretic administeration of narcotics a direct action of narcotics on neurons active in the regulation of ventilation will be described. The effects of narcotics on the activity of neurons with respiratory related activity will be compared with those observed with non-respiratory neurons which respond in a specific manner to increases and decreases in carbon dioxide levels. Similar investigations will examine the effects of endorphins on the activity of these neurons. Localization of narcotic sensitive and endorphin sensitive neurons will also be made with regard to discrete sites in the brainstem which participate in the control of ventilation.